Heat transfer experiments were performed in a reactor, which was built to simulate the mixing between particles and particles in the entrance zone of a downer reactor being applied in the ‘coal topping process’ developed at Institute of Process Engineering, Chinese Academy of Sciences. Superficial heat transfer coefficients were measured with a ball probe. The experimental results show that the heat transfer coefficient increases with the bed temperature and the solid holdup, and decreases with the diameter of bed materials. A semi-empirical heat transfer coefficient correlation was obtained based on dimensionless analysis, taking into account the effect of the important operating parameters under simulated downer entrance conditions. The results calculated from the correlation show a fair agreement with the experimental data. The correlation was applied to estimate the heating rate of the coal particles used in a bench scale experimental apparatus for studying the coal topping process.

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